Herpes simplex virus is the leading cause of blindness due to infectious disease in the United States. Several antivirals are currently approved for treating HSV keratitis but there are problems with their use and some infections are refractory to treatment. These antivirals also cannot eliminate latent infection and recrudescent infections cause the majority of the blinding keratitis. Strategies that act on virions themselves to prevent attachment or entry into cells are viable strategies that have not been adequately studied. We previously described several peptides that inhibit HSV infection at low micromolar concentrations by inactivating virions in solution, inhibiting entry, and inducing a state of resistance in cells pre-treated with the peptides. These peptides also show little if any toxicity in the eye. Recently, we described a peptide, TAT-C, that inhibits HSV-1 infection and preliminary data suggests TAT-C binds to sialic acids on viral envelope proteins. A second critical finding recently published, is that sialic acids on one or more HSV-1 entry proteins are required for efficient entry into cells. These findings lead us to propose the overall hypothesis that TAT-C inhibits HSV fusion by binding to sialic acids on one or more entry proteins and that this binding interferes with a sialic acid mediated step in the entry process. The experiments in this proposal are designed to test this hypothesis and will be accomplished through four specific aims. 1) Test the hypothesis that TAT-C and sialic acids are involved in an entry step prior to fusion. 2) Test the hypothesis that TAT-C or removal of sialic acids from gB, gD, and/or gH/gL alters the function of the proteins. 3) Test the hypothesis that TAT-C or sialic acid removal alters the structure or stability of gB, gD, and/or gH/gL. 4) Test the hypothesis that sialic acids are critical for in vivo infection and that TAT-C has in vivo efficacy and the effect on latency. These studies will increase our understanding of the role of virion sialic acids in HSV-1 infection and could lead to the development of novel antiviral strategies for therapy. PUBLIC HEALTH RELEVANCE: We describe studies that will determine how sialic acids on HSV-1 envelope glycoproteins affect ocular disease and the role they play in viral entry. We will also test the mechanism whereby a peptide that binds sialic acid blocks HSV-1 infection. The studies will provide new insights into HSV-1 entry and could lead to the development of novel antivirals.